This invention is related to the reinforcing of vinyl chloride ("VC" for brevity) homopolymers with glass fibers, in the field of improving the physical strength characteristics of organic synthetic resinous materials. More particularly, this invention is related to thermoplastic, glass fiber reinforced ("GFR") poly(vinyl chloride) ("PVC") homopolymer, and chlorinated poly(vinyl chloride) ("CPVC") which homopolymers are commonly available as rigid PVC and CPVC, and are either individually or together referred to herein as "VC homopolymer".
More generally this invention is directed to copolymer of VC with a copolymerizable monomer, in which copolymers VC is present in an amount sufficient to generate an allylic chlorine (Cl) moiety in the VC chain, represented thus: EQU --CH.sub.2 --CHCl--CH.dbd.CH--CH.sub.2 --CHCl--CH.sub.2 --CHCl--
under thermoforming conditions. The copolymers may be postchlorinated provided there are sufficient runs of 10 or more C atoms in VC chains to generate reactive allylic Cl moieties. Such copolymers of VC, optionally postchlorinated, and VC homopolymer are generically referred to herein as "VC resin".
This invention is more particularly related to the use of an aminosilane coupling (or keying) agent (sometimes referred to as `finish`) which is essential, in combination with certain polymeric film formers used in the production of glass fibers, most preferably E glass, to provide the strength in our glass fiber reinforced ("GFR") VC resin composites.
It is well known that the key to providing satisfcatory strength in a GFR composite is the proper choice of "size" or "sizing" on the glass fibers which are coated with an aqueous sizing solution, suspension, or emulsion consisting essentially of water in which is dispersed a coupling agent, film former, lubricant, surface active agent, "antistat", plasticizer and the like, sometimes with a water-soluble colloid to provide the necessary stability for the dispersed polymeric film former. It is most important to use the correct combination of coupling agent and film former in the "size".
Glass fibers sized for use in our invention may be used in strands, rovings, tow or yarns, which are treated specifically for use in a GFR thermoplastic resin. Unsized glass fibers are also referred to as untreated, pristine, or bare glass.
The most widely used size for glass fibers used in GFR composites for general purpose reinforcing of resins contains a suspension of poly(vinyl acetate) particles in an aqueous medium. Polyesters, epoxides, poly(methyl methacrylate) and polystyrene are also used as film-formers sometimes on their own, sometimes as separate additives to the size, and sometimes as a copolymer with poly(vinyl acetate). No film former was considered to have a reactive or catalytic function in the composite.
The essential qualification of a size found satisfactorily to fulfil the strengthening function of glass fiber in VC resin is its (the size's) ability to generate allylic chlorine (Cl) moieties in a zone adjacent the surface of each glass fiber ("fiber-resin interface") where the moieties can react with the primary amine moiety of the coupling agent. This concept is taught and illustrated in U.S. Pat. No. 4,536,360 to Rahrig, the disclosure of which is incorporated by reference thereto as if fully set forth herein. The specific effective combination disclosed therein for a VC resin is (a) an aminosilane coupling agent, and, (b) a polymer film former of a ring-opened lower alkylene oxide containing 1 to 4 carbon atoms as an essential component in a repeating unit, for example poly(ethylene oxide:propylene glycol) ("PEO"), optionally containing another copolymerizable component.
Though the criticality as to the choice of PEO as the film former was recognized in the '360 patent, the function of PEO in catalyzing the formation of allylic Cl moieties, unrelated to that of the aminosilane, was not known, nor was the mechanism known by which that function was discharged. Since it is well known that the silane groups of the aminosilane are coupled to the surface of the glass leaving the amino groups projecting therefrom, it was hypothesized the PEO had a unique shrouding effect which did not adversely affect the reactivity of the amino groups which are known to generate the allylic Cl moiety. This hypothesis did not help us to define either the essential reactive function of a satisfactory film former (to be used in conjunction with an aminosilane in the size), or the film former's essential characteristics and generic structure.